Ok. Some basic rules. The derivative of a constant is zero. That could be 1,2,3, pi, e, phi, etc. - the derivatives of all of these are zero.

If you have a polynomial in the form of $\displaystyle y=x^n$, then $\displaystyle y'=nx^{n-1}$ So you can apply both of these rules to your f(x),g(x), and r(x).

On k(x), is that supposed to be $\displaystyle 15x^{\frac{2}{3}}$, or $\displaystyle 15x*\frac{2}{3}$? I can't tell. And on the second f(x) term, is that supposed to be $\displaystyle \frac{\sqrt{x+1}}{\sqrt{x-1}}$?